Synthetic bristle and process for its production



Jan. 26, 1954 F. J. 3. OLMER ET AL 2,666,976

SYNTHETIC BRISTLE AND PROCESS FOR ITS PRODUCTION Filed June 10, 1950 STRETCHED MONOF/L F'ICiZO SPINNING MONOF/L SPINNERET F/LAMENTS RES/N SOLUTION INVENTORS. FRANCOIS J.G.OL MER BY GLENN A. NESTY ATTORNEY.

Patented Jan. 26, 1954 UNITED STATES PATENT OFFICE SYNTHETIC BRISTLE AND PROCESS FOR ITS PRODUCTION New York Application June 10, 1950, Serial No. 167,373

14 Claims. 1

This invention is directed to processes for the production of bristles of a polymer of acrylonitrile containing at least 70% acrylonitrile and. the remainder substantially consisting of an acrylic compound polymerizable with acrylonitrile, and to the bristles produced by these processes.

Bristles are characterized by their being monofils, i. e. unitary filaments, generally 0.5 mil or more in diameter. As a result of their unitary structure bristles have quite different characteristics with respect to stiffness, resilience to bending while still flexible, and the like, from yarns or threads of similar size but made up of a mass of individual fibers held together by irregularities in the shape or surface of the fibers or by a twist of the yarn or thread. The term bristle, therefore, in this specification and in the claims refers to a unitary filament or monofil of the order of 0.5 to 50 mils diameter having the commonly recognized characteristics of bristles and are of diameters suitable for being made up into brushes, as distinguished, on the one hand, from threads or yarns which have little resilience, and, on the other hand, from rods which have larger diameters and less flexibility.

For a great many years practically the only source of bristles was the coarse hair of various animals, such as hog bristles or horse hair bristles. Of late years, however, it has been proposed to produce bristles from artificially prepared thermoplastic resins. It has, however, been an exceedingly diificult problem to find suitable synthetic resins for the purpose, and to process those resins so as to convert them into filaments whose properties are suificiently similar to those of natural bristles for the latter to be satisfactorily substituted by those artificially produced. For example, artificial bristles have been commercially manufactured from cellulose acetate. One difficulty with bristles of these materials is their solubility in solvents which may come into contact with the brushes made of such bristles. This is particularly true in the case of paint brushes. Certain of the solvents in paint or lacquer or among those commonly used for cleaning paint or lacquer from brushes, will destroy the bristle by solvent action thereon. 7

Other characteristics of suitable bristles, predominantly determined by the bristle material itself, include resistance of the bristle to repeated flexing without breaking or cracking, its ability to repeatedly bend without permanent deformation, and to return to its original straight condition without loss of stiffness.

terials with good stiliness would be The bristle ma- 55 terial should be wetted by the different types of liquids in connection with which a brush is to be used without, however, dissolving in the liquid or being otherwise alfected thereby. The material must be resistant to the abrasion to which bristle brushes are subjected in use.

To find a material whose properties are good with respect to all of the factors important in a bristle, is exceedingly difficult. This is in part 10 due to the fact that materials which have one characteristic, such as resistance to permanent distortion on bending, generally have poor characteristics in other important respects, such as resistance to abrasion and stiffness. Other maexpected to have low flexibility and poor resistance to breaking or cracking when repeatedly bent.

Certain polymeric materials are characterized by a combination of properties peculiarly suitable for bristles in the respects important thereto. These materials are resins essentially composed of the acrylonitrile polymers containing at least 70% by weight of acrylonitrile and the remainder an acrylic compound polymerizable therewith. These polymers include polyacrylonitrile itself and the copolymers containing at least 70% acrylonitrile copolymerized with an acrylate ester, such as methyl or ethyl acrylate or the acrylic esters of higher aliphatic alcohols,

3 withJ acrylic nitriles other than acrylonitrile,

such as the alpha-alkyl acrylic acid nitriles, a

representative member of this group being methacrylonitrile, or with the esters of an alphaalkyl acrylic acid, such as methyl or ethyl methacrylate or methyl ethacrylate. We have found that a copolymer of methacrylonitrile and acrylonitrile in the proportions of 10/90 to 30/70 parts by weight of methacrylonitrile to acrylonitrile is a particularly good polymer for making bristles.

The bristles of these resins may be non-homogeneous as a whole. For example, they may have another material on or imbedded in the surface of the bristle. Nor in referring to a resin essentially composed of the above polymers is it inthe character of the acrylonitrile polymer resin.

In addition to the important properties of bristles which result from the composition of the materials of which they are made, there are a number of other properties which depend upon the physical character of the bristles and hence on the process employed in converting a resin into bristles. For example, it has long been recognized that in paint brushes made of hog bristles, small irregularities of the hog bristle surfaces which are lacking to a large degree in brushes made of horsehair, aid in the brush picking up and holding paint or other liquids and regulating the flow of the liquid from the brush to a surface over which it is drawn. An important characteristic of good bristles for paint brushes is that the individual bristle ends split into a number of smaller filaments, the so-called flagging or the bristles. In use, the rubbing and flexing of the bristle ends on the surface'being painted should renew this flagging as the bristle ends are worn away. This is important in spreading paint without leaving brush marks. While this flagging of the tip of the bristles is highly desirable, it is even more important that the splitting of the bristle occur only at the end and not travel far up the bristle length to destroy the desired flexing characteristics of the bristle body.

We have discovered a new process for producing bristles from the above-described acrylonitrile resins and from our polymeric methacrylonitrile-acrylonitrile resins in particular, which priduces bristles of a physical structure particularly desirable with respect to the important characteristics referred to above. By our preferred process we produce bristles having a nonuniform, creviced surface which increases the capacity of a brush made of those bristle to pick up and hold liquids. Our process permits producing bristles with or without flagged ends depending upon whether they are to be made up into paint brushes, for example, where the flagged ends are desirable, or into other type brushes where the flagging of the bristle ends may be unimportant or undesirable. The bristles may be of uniform size throughout their length, or may taper towards one end, depending on the flexing characteristics of the type of brush for which the bristles are to be used.

Our process for making bristles involves dissolving the acrylonitrile polymer in a solvent for the polymer to obtain a solution of suitable viscosity for spinning into filaments. The preferred viscosities are in the range 45,000 to 400,000 centipoises. Preferably, a solution of copolymerized methacrylonitrile-acrylonitrile resin in dimethyl formamide having a viscosity in the foregoing range, is prepared. The resin solution is spun from a spinneret having numerous individual holes. The number and size of the holes are so chosen as to give a bundle of filaments which together form a bristle of desired cross-sectional size of 0.5 to 50 mils diameter. Differences in the size and spacing of theholes in the spinneret permit varying the structure of the bristle. For example, by having all the holes arranged in a circle, bristles with internal void spaces may be produced, if desired. For paint brush bristles it is desirable to avoid a hollow structure and we have discovered this may be accomplished by having at least one hole within the circle. As a specific example for spinning solutions to obtain bristles for paint brushes, we preferably employ spinning solutions containing about to about of a polymeric rnethacrylonitrileacrylonitrile resin containing 10/90 to /70 by weight methacrylonitrile/acrylonitrile resin in dimethyl formamide and a spinneret with holes 10-15 mils in diameter, with all but one of the holes arranged in a circle and that one within and 4 at about the center of a circle defined by the other holes.

The plurality of filaments are drawn from the spinneret through a solvent removal zone in which a part of the solvent is removed from the individual filaments either by vaporization into air or other gas, by extraction with a liquid in which the solvent is soluble or by any combination of both extraction and vaporization of the solvent. From this solvent removal zone the filaments are drawn through a drying zone in which most or nearly all of the residual solvent is removed by heating the filaments in air or other gas inert thereto.

Between the zone of partial solvent removal and the drying zone the several individual filaments are gathered into a bundle or yarn of contiguous filaments. The point between these two zones at which the filaments are gathered together is determined by the character of the resin, the solvent used in making up the spinning solution, the size and rate of drawing the filaments, the solvent extraction or evaporation means employed in the zone of partial solvent removal. and the temperatures attained in the drying zone. The point of gathering is where the amount of residual solvent left in the filaments i sufficient to render them tacky, so that when gathered they adhere and after drying to remove residual solvent the several filaments are bonded into a unitary, monofil structure. The bond thus formed is suficiently firm for it to be retained throughout the main body of the monofil when out into bristles which are subjected to flexing in use. In making bristles for paint brushes or other uses where an irregular creviced or corrugated surface is desirable, the point of gathering is further limited to one where the solvent remaining in the filaments is insufficient to cause them to coalesce into a single larger filament of uniform configuration, but rather to bond together into a monofil which retains the creviced or corrugated surface configuration characteristic of a plural ity of individual filaments bonded together.

Our process is especially adapted to the production of bristles with this creviced or corrugated surface. By spinning a plurality of filaments from a resin solution and first removing a portion of the solvent by extraction or evaporation while the filaments are separated, the solvent content in the surface layer of the filaments is reduced while retaining a relatively high content of solvent in the interior of the filaments. When a plurality of such filaments are brought together into a bundle in which they are in close contact with each other, as the solvent migrates from the interior to the surface of the several filaments, we have found it is practicable to evaporate the solvent at elevated temperatures without the filaments becoming so plastic that they fuse into a uniform monofil with smooth surfaces, Under solvent evaporation conditions practicable to maintain in a plant, we have found the migrating solvent may be evaporated from the bunched filaments to cement the filaments together into a monofil while still retaining a residual structure of the several filaments to the extent nccessary to give the desired corrugated or creviced surface; or even further, to the extent necessary to retain within the monofil itself lines of cleavage between the filaments which permit flagging cut ends of the monofil without the body of the monofil breaking down along these lines of cleavage under the stresses to which bristles are normally subjected.

The point of gathering the filaments, which marks the dividing line between the zones of partial solvent removal and of drying at an elevated temperature to remove residual solvent, may be at or below the surface of a liquid bath into which the filaments are spun from the spinneret, in a space through which the filaments travel in passing from the spinneret or liquid spinning bath to a drier, or even in a part of the drier through which the filaments first travel and are heated to evaporate a portion of the solvent before being gathered and further heated to complete the removal of. solvent.

In many cases special means for thus gathering the several filaments into a bundleneed not be provided. When the filaments pass from the spinneret into a liquid bath, the mutual attraction of the small filaments wetted with the liquid of the spinning bath may serve to gather the filaments together at a proper distance from the spinneret surface. Variations in the size and spacing of the holes of the spinneret, the depth of the spinning bath over the spinneret face, rate of drawing the filaments, composition of the resin solution supplied to the spinneret, and other factors influence the distance from the spinneret face at which the filaments gather into a single strand or bundle without the provision of special means for that purpose.

While the point at which the individual filaments are gathered into a bundle varies with the polymer and solvent employed and spinning conditions maintained in operating our process, it is a very simple matter to determine the proper point at which the filaments should be gathered and to adjust operating conditions to so gather them. Thus, if in operating the process the monofil after drying does not have the desired irregular surface configuration, it means insufiicient solvent has been removed before the filaments are gathered and the point of gathering is moved farther from the spinneret to allow additional evaporation or extraction of the solvent. If, on the other hand, the bond between the individual filaments making the monofil is too weak so that under repeated flexing the filaments tend to separate in the body of the bristle and the bristle loses its desired strength, resilience, etc., the point of gathering the filaments is moved closer to the spinneret so that less solvent is evaporated before they are gathered together, thus increasing their tackiness and the strength of the bond between the filaments after removal of the residual solvent by the drying step. When the filaments are wet spun so they tend to gather by mutual attraction, by more rapidly drawing the filaments from the spinneret to the drying zone or employing a wider spacing of the holes of the spinneret, the point at which the filaments gather into a bundle may be moved farther from the spinneret. When a pig tail or other positively acting gathering device is employed it is moved toward or away from the spinneret as required.

The gathered bundle of filaments is drawn through a heater to dry the filaments by evaporation of solvent therefrom. By this evaporation of solvent at elevated temperatures the fibers are bonded into a unitary monofil. Most of the solvent evaporates quite readily from the monofil during continuous passage through a heater without having to use unduly high temperatures, such as would deleteriously. affect the polymeric material, or unduly increase the length of travel through the heater. However, the monofil tends obtained by annealing the monofil either before orafter it is stretched.

This annealing step is essentially a slow drying step for removal of additional solvent from the monofil to give it the desired added stiifness. It is best accomplished by winding the dried monofil on reels or otherwise forming it into suitable packages or bundles for heating in an oven at about C. to reduce further the solvent content of the monofil. The time required will depend upon the temperature in the oven,

circulation of a drying atmosphere of air or other inert gas through the oven; and other factors known to affect the rate of drying a material containing a volatile liquid. When the annealing follows a stretching or tapering step, the monofil is held under sufiicient tension while being heated to prevent it shrinking enough to destroy the effects of the stretching or tapering operation.

In stretching the monofil to molecularly orient it and to increase its tensile strength, the conditions employed are those suited for stretching filaments, threads or rods of the particular resin of which the monofil may be formed. As is well known for various types of resin, the stretching may be carried out at temperatures above atmospheric but below the temperatures at which the resin is too soft for orientation by the stretching.

When it is desired to produce tapered bristles this may advantageously be done simultaneously with stretching the monofil to molecularly orient it. In so doing the monofil is heated and is stretched by passing through a, hot zone of short length to which the monofil is fed or from which it is drawn at alternately increasing and decreasing rates of speed. The monofil of uniform size I is thus converted into one with alternating thick and thin portions with the greatest effect of the orientation in increasing the strength of the bristles being centered in the thinner portions which are stretched the most.

The monofil produced by drying the bundle of filaments, either with or without the additional treatments described above, of annealing, stretching or tapering, is cut into suitable bristle lengths. For tapered bristles, the monofil which has been stretched to form alternating thick and thin portions, may be cut at the thin portions. Each length thus obtained is doubled on itself to form two bristles connected together at their thicker, butt ends. By cutting the monofil both at its thin and thick portions, individual tapered bristles are obtained.

The accompanying drawings illustrate in Fig. 1 our preferred process for producing bristles from solutions of the acrylonitrile polymer resins. Fig. 2 is a view of the face of the spinneret I of Fig. 1, showing our preferred arrangement of the holes of the spinneret. Fig. 3 is a view of a single tapered bristle particularly suited for paint brushes produced by our preferred process. Fig. 4 is a cross-section along line 4 of Fig. 3, showing the corrugated or creviced surface of the bristles produced by our preferred process, whether they be tapered or untapered.

the resin solution to be treated is soluble but the ni m ol a hen t i li id is-we en it is preferably covered with a thin oillayerj, A

1, the numeral l insolution o he r itr e el' ne nascl ent I therefor is supplied to spinneret l and extruded in the form of numerous H The filaments pass through the layer of liquid overlying the spinneret depth to extract a portion of the solvent from the resin solution, sufficient to form on each filament a surface skin of coagulated resin strong enough for the filaments to be drawn from the liquid bath without undue breakage. Means not shown in the drawing are provided to Withdraw liquid containing solvent from cup 3 and to supply fresh liquid theretoso as to maintain a low concentration of solvent in the bath and its effectiveness to extract solvents from the filaments.

Under some conditions for treating a resin solution herein described, the mutual attraction of the wetted filaments themselves may be sulficient to draw them together at the bath surface while they contain enough solvent to insure that a homogeneous monofil be formed. A pigtail l is provided in the apparatus illustrated in the drawing, which may be used to vary the point at which the filaments are brought together and thereby act as a control for the degree of bonding between filaments. After a short travel through air the bundle of filaments enters an electrically heated drier 6 and is drawn through the axial drying chamber within the drier. .By evaporation of solvent at the elevated temperatures in heater 6, the bundle of filaments is cemented together or fused into a monofil 13. A positively driven draw wheel 8 serves to draw the filaments continuously from the spinning bath through fil over two free running pulleys or wheels 9 and 10 at a substantially constant speed.

The'monofil may be taken from draw wheel 8 and cut into suitably short lengths to convert it into bristles. When it is desired to molecularly orient the resin composing the bristles, the monofil is passed from draw wheel 8 through a heater It to a second positively driven draw wheel H whichis rotated at a peripheral speed greater than that of draw wheel 8. The monofil is thus drawn from the heater by wheel H at a rate greater than that at which it is. passed thereto by wheel 8. In passing through heater lo the monofil is heated which it is 'molecularly oriented by the stretching of the monofil which takes place in this heater. The thus stretched and oriented monofil drawn from wheel ll may be cut into suitable bristle lengths.

In order to make the tapered bristles illustrated in Fig. 3 of the drawings, heater lilis short so that the heating of the monofil to stretching temperatures is concentrated along a short section of the path of the monofil through the heater. Between snubber wheel 8 and draw wheel H the monofil passes under two freely rotating pulleys l3 and I5 and over a freely roindividual filaments.

u a for fi e ent the d ier n th lt ng m o:

to temperatures at tating pulley l4. Pulley I4 is attached by .a flexible wire or cord l9 running over a pulley 15 to a pin 18 carried on the face of a driven wheel ll. Pin 18 is set oif center on wheel I! so that, as the wheel rotates, pulley M is alternately raised and lowered.

The monofil passes over wheels 8 and H at constant but different speeds, that at wheel H being greater than that at wheel 8. The alternate raising and lowering ofpulley l4 periodically increases and decreases the length of the path of the monofil in goingfrom wheel 8 to wheel H which represent points in its travel at which itis moved at constant but different speeds. These periodic changes in the length of the path cause correspondingly periodic.

changes in the amount successive portions of the monofil are stretched in passing through the heater and produce recurring differences in cross-sectional size of the monofil; it being smallest in those portions passing through the heated region in heater l6 when pulley M is ascending at its maximum rate (when wheel I! is in the position shown in Fig. 1) and largest when pulley i4 is descending at its maximum rate (a half turn later of wheel ll). Between the sections of maximum and minimum diameters of the monofil, it tapers from one size to the other. The degree of orientation of the resin is directly related to the amount it is stretched. Accordingly, the thin portions of the monofil, where high strength is most desirable,.are more highly oriented and strengthened than the thicker portions, where increased strength by stretching is less important. In fact, the thicker portions need not be stretched at all or even have been shrunk while in the heated zone by operating so that when pulley I4 is descending at its maximum speed, the monofil momentarily is passed to heater H1 at a speed somewhat greater than that at which it is drawn therefrom-by wheel H.

Similar tapering of successive portions of the monofil passing through heater [0 may be obtained by employing other means to periodically change the amounts the short heated sections of the monofil are stretched. For example, instead of employing the movable pulley i l in the manner described above, draw wheel ll may be driven at periodically increasing and decreasing speeds. In the particular arrangement of apparatus illustrated in Fig. l, pulley I4 is placed ahead or heater l0 and changes the amount of stretch imparted to the monofil by changing the rate of passing the monofil to the heated zone in which it is stretched. By placing pulley M after the heater, periodic changes in the amount of stretching the monofil are also obtained by periodically varying the rate at which the monofll is drawn out of the heated zone. tions along the length of the monofil.

The monofil delivered from draw wheel H is taken up on a reel [2. The diameter of reel I2 is such that portions of the monofil of largest diameter are placed in contiguous rows. By cutting across the contiguous thick and thin portions, bristles are obtained having the tapered configuration shown in Fig. 3.

The thin ends of the bristles may be flagged for a short distance as shown in Fig. 3. his flagged end is produced by flexing the bristle ends by frictional forces, by axially compressing the bristle ends to repeatedly sharply bend them, or by otherwise breaking the bond between fila- This also produces periodic tapered por-v ments in the bristle ends either before or after the bristles are made up in the form of a brush. As shown in Fig. 3 and the cross-sectional view of Fig. 4 taken along line 44 of Fig. 3, the individual bristle has a unitary structure, with the longitudinally creviced or corrugated surface configuration of a bundle of numerous contiguous filaments extending lengthwise from end to end of the bristle. In cross-section the bristle is approximately oval or rectangular with rounded corners. It has a scalloped outline.'

A non-flagging bristle may be made by reducing the depth of the water spinning bath or by moving the point of gathering the several individual filaments closer to the spinneret face, to a point where sufficient solvent has been evaporated to prevent coalescence of the filaments while still leaving enough solvent to increase the bond between the filaments so that the bristles no longer flag when subjected to flexing.

Other modifications in the process and resulting diiferences in the bristle products may be made without departing from the scope of our invention as described above and as illustrated by the following particular procedures:

Example I.A copolymer is prepared by mixing 20 parts methacrylonitrile, 80 parts acrylonitrile and 1400 parts of water with vigorous stirring to disperse the monomers in the water at 35 C. under an atmosphere of nitrogen gas. To this monomer dispersion there is added and dissolved therein 1.5 parts potassium persulfate and 0.45 part sodium metabisulfite. (Throughout this specification parts referred to are parts by weight.) The suspension is then stirred for 2 hours following addition of the persulfate-metabisulfite catalyst, with the temperature being maintained at 35 C. The methacrylonitrile and acrylonitrile copolymerize to form a suspension or latex of polymer particles dispersed in the aqueous reaction mixture. The polymer latex is coagulated by freezing it. The coagulated polymer is filtered from the aqueous mother liquor, washed with water and with methanol and dried.

A copolymer thus prepared had an intrinsic viscosity of 3.27. The intrinsic viscosities given in this application are those determined for a solution of 0.125 gram of the polymer per 100 cc. of solution of the polymer in dimethyl formamide, employing Ostwald-Fenski tubes. The numerical values for the intrinsic viscosities are calculated using the equation:

Time of efliux of solution-time I of efllux of solvent ntnnslc Vlscosl 0.125 Tirne of efi-lux of solvent A 15% solution of this copolymer in dimethyl formamide had a viscosity of 120,000 centipoises at 30 C.

This solution was spun into filaments through a spinneret having 10 holes, each 10 mils in diameter, into a water bath 1% inches dee above the face of the spinneret. The water was covered with a 4; inch layer of toluene. The filaments gathered into a bundle at the water bath surface, which was drawn through electrical driers at the rate of 8 feet per minute. The bundle of filaments traveled first a distance of about 5 feet through a drier maintained at about 140 C. and then for a distance of about 6 feet through a drier maintained at about 175 C. In this and the following examples, the drier, heater or oven temperatures were those recorded at the point of maximum temperature of the air space inthe drier, heater or oven through which the monofil was drawn. From a draw wheel corresponding to draw wheel 8 of Fig. 1 of the drawings, driven-at a peripheral speed of 8 feet per minute, the resulting monofil was passed under pulley I3, over pulley l4 and under pulley l5 and thence drawn by a wheel ll through oven it, 5 inches long. Pulley M was alternately raised and lowered by means of the driven wheel 17 having the center of pin 18 set 1 inch from the center of rotation of the wheel. Wheel I! was rotated at the rate of 30 revolutions per minute. Draw wheel H was driven at a peripheral speed of 20 feet per minute. Heater H! was maintained at about 180 C. The resulting monofil, having alternating tapered and reverse tapered sections was Wound up on reel l2. When the monofil was cut at its thick and thin points bristles tapering from about 6.8 mils diameter to about 4.3 mils diameter through a distance of 7.8 inches were obtained. They had the corrugated surface configuration illustrated in Figs. 3 and 4 of the drawings.

Example II.-A 20/80 copolymer of methacrylonitrile and acrylonitrile was prepared by a procedure essentially similar to that used in the preparation of the copolymer of Example I, differing therefrom in the following respects: The methacrylonitrile and acrylonitrile were mixed with 1700 parts of water at 60-65 C. and 0.54 part potassium persulfate and 0.096 part sodium metabisulfite were added as catalyst. The suspension was stirred at (ii-67 for 5 hours following addition of the catalyst. The copolymer thus prepared had an intrinsic viscosity of 4.21. A 13% solution of the copolymer in dimethyl formamide had a viscosity of 120,000 centipoises at 30 C.

This copolymer solution was spun through a spinneret having 10 holes, each 10 mils in diameter, into a water bath 1 inch deep over the face of the spinneret covered with a inch layer of benzene. The filaments gathered together at the bath surface into a bundle which was drawn at the rate of 5.2 feet per minute through a drier 3 feet long heated at 158 C. From a draw wheel corresponding to wheel 8 of Fig. 1 of the drawings, rotating at a peripheral speed of 5.2 feet per minute, the resulting monofil was drawn directly through a heater H] which was 3 feet long, by a reel I2 rotating at a peripheral speed of 10.5 feet per minute. Heater ID was operated at about 201 C. The monofil was stretched The monofil on reel I2 was heated in an oven for 3 hours at C. and then cut into short bristle lengths. Y M

In cross-section the bristles thus prepared were approximately rectangular, with scalloped. surfaces as shown in Fig. 4. The longer and shorter diameters of the bristle cross-section were 6.5 and 4.7 mils, respectively. The bristles were made up into a brush and by mechanically working or stressing the bristle ends they were flagged.

Example IIL-A copolymer is prepared by mixing 20 parts methyl methacrylate, 80 parts acrylonitrile and 450 parts water with vigorous stirring to disperse the monomers in the water. To this monomer dispersion at 35 C., 1.30 parts ammonium persulfate and 0.3 part sodium metabisulfite are added and dissolved and the mixture maintained at temperatures in the range 35 to 40 C. for a period of one hour. The resulting polymer is recovered from the mother liquor, washed with water and methanol and bending the ends of trated in Fig. 3.

bath surface and the rate of 10.5 feet per minute through three driers Y (each area long) heated in sequence at 15759, "-'-13'7 -C.- and 1'72" C. The rsulting'monofil was cut ihto -bristle lengths.

nierizable therewith; said polymer dissolved in partially removing --formamide is made up having an intrinsic viscosity of 213,000 centipoises at 30 C. This solutionis spun from a spinneret having I I holes, each mils diameter, one of the holes being at the center of the spinneret and the remaining ten --placed in a circle thereabout. The filaments leaving the spinneret pass upwardly through a water bath 2 /2 inches deep. The several filaments gathered together at the bath surface and the filament bundle was drawn in series through four ovens heated in sequence, in the order in which the bundle of filaments was drawn therethrough,

"813151" (3., 138 C., 158 C., and 157 C. The tow of filaments and monofil was drawn from the spinneret through the ovens at the rate of 10.5

"feet per minute, measured at a draw wheel around which the monofil leaving the last oven was "passed.

'The'monofil thus produced is tapered by the procedure described heretofore in connection with Example I, the heater employed for heating the 'inonofil to stretching temperatures being maintained at 175 C. A monofil thus produced had recurrently tapered sections from about 9 mils diameter at their thickest portion to 4 mils diameter at their thinnest portions and the distance Bristles cut from this monofil have the corrugated surface illustrated in Figs. 3 and 4 of the drawing. By repeatedly the bristles they fiag as illus- Erample IV.100'parts acrylonitrile were suspended by vigorous stirring in 523 parts water.

To this suspension 1.62 parts potassium persulfate and 0.288 part sodium metabisulfite were "added and the suspension stirred at 47-53 C.

for about 15 minutes. The resulting slurry was filtered and the solids washed with water and methyl alcohol and then dried. The polyacrylonitrile thus prepared had an intrinsic viscosity of 5.41.

A 10% solution of this polyacrylonitrile in dimethyl formamide was made up and spun through the spinneret employed in'carrying out Example III, the filaments passing upwardly through a water bath 2% inches deep at 25 C. The several filaments gathered into a bundle at the water bundle was drawn at the These bristles had the corrugated surfaces heretofore described. B'y

fiexihgthe bristle ends they were flagged as shown-in Fig. s-or the drawings.

W'claim: 1

1. The process for producing a monofil suit- 'able for cutting into short lengths having the characteristics of bristles which comprises spinnin'gnumerous separated filaments from a solution of a polymer of acrylonitrile containing at least 70% acrylonitrile and the remainder substantially consisting of an acrylic compound'poly solution containing the a volatile solvent therefor, solvent from the separated filaments, gathering the filaments into a bundle of contiguous filaments while they still contain a portion of the solvent of said solution, and drawingsaid bundle of contiguous filaments through a zone in which they are heated at elel2 vated temperatures at which solvent contained in the bundle of filaments is evaporated into a gaseous atmosphere in said zone and the filaments bond together into a unitary monofil without application to said bundle of external pressure forcing the filaments together, said filaments of acrylonitrile is polyacrylonitrile.

4. The process for producing bristles which comprises spinning numerous separated filaments froma solution of a polymer of acrylonitrile containing at least '70 acrylonitrile and the remainder substantially consisting of an acrylic compound polymerizable therewith, said solution containing the polymer dissolved in a volatile solvent therefor, partially removing solvent from the separated filaments, gathering the filaments into a bundle of contiguous filaments while they still contain a portion of the solvent of said solution, drawing said bundle of contiguous filaments through a zone in which they are heated at elevated temperatures at which solvent contained in the bundle of filaments is evaporated into a gaseous atmosphere in said zone and the filaments bond together into a unitary monofil without application to said bundle of external pressure forcing the filaments together, said filaments being gathered at a'point at which they contain sufficient solvent to cause the individual filaments to bond together by said evaporation of solvent during said heating into a unitary monofil which retains the corrugated surface configuration of a bundle of contiguous filaments, and cutting the monofil into short lengths.

5. The process for producing bristles which comprises spinning numerous separated filaments from a solution of a polymer of acrylonitrile containing at least acrylonitrile and the remainder substantially consisting of an acrylic compound polymerizable therewith, said solution containing the polymer dissolved in a volatile solvent therefor, partially removing solvent from the separated filaments, gathering the filaments into a bundle of contiguous filaments while they still contain a portion of the solvent of said ments in'a' g'aseous' atmosphere at elevated temperatures and thereby -'ev'aporating solvent from the bundle of filaments, said filaments being gathered at a point at which they contain sufficient solvent to cause the individual filament to bond together during said heating into a unitary monofil without external pressure forcing the filaments together being" applied to the bundle of filaments, continuously passing said monofil through a heating zone in which short portions of the monofil successively passed therethrough are heated, stretching the thus heated monofil, periodically changing the amount successive portions of the monofil are stretched, thereby forming along its length alternating sections of large and small diameters with the monofil tapering from one to the other of these sections, and cutting the monofil at its points of smallest diameters to form tapered bristles.

6. The process for producing bristles which comprises spinning numerous separated filaments from a solution of a polymer of acrylonitrile containing at least 70% acrylonitrile and the rema nder substantially consisting of an acrylic compound polymerizable therewith, said solution containing the polymer dissolved in a volatile solvent, therefor, partially removing solvent from the separated filaments, gathering the filaments into a bundle of contiguous filaments while they still contain a portion of the solvent of said solut on, heating said bundle of contiguous filaments in a gaseous atmosphere at elevated temperatures and thereby evaporating solvent from the bundle of filaments, said filaments being gathered at a point at which they contain sufficient solvent to cause the individual filaments to bond together during said heating into a unitary monofil which retains the corrugated surface configuration of a bundle of cont guous filaments without external pressure forcing the filaments together being applied to the bundle of filaments, continuously passing said monofil through a heating zone in which short portions of the monofil successively passed therethrough are heated, stretching the thus heated monofil, periodically changing the amount successive portions of the monofil are stretched, thereby stretch ng the monofil to molecularly orient it and forming along its length alternating sections of large and small thickness with the monofil tapering from one to the other of these sections, and cutting the monofil at its points of smallest diameters to form tapered bristles.

7. The process of claim 6 wherein the polymer of acrylonitr le is a copolymer of methacrylonitrile and acrylonitrile copolymerized in the ratio of 10/90 to 36/70 by weight of methacrylonitrile/acrylonitrile.

8. The process of claim 6 wherein the polymer of acrylonitrile is polyacrylonitrile.

9. Bristles of a polymer of acrylonitrile containing at least 70 acrylonitrile and the remainder substantially consisting of an acrylic compound polymerizable therewith, said br stles having a diameter of 0.5 to 50 mils, with the body of the individual bristles having a homogeneous structure of said polymer and the corrugated surface configuration of a bundle of numerous contiguous filaments extending lengthwise from end to end. of the brstle, and the bristle in crosssection having a scalloped outline, said homogeneous tructure within the body of aid bristles having een formed by spinning numerous separated filanints from a solution of said polymer in a volatile solvent therefor, partially removing solvent from the separated filaments, gather ng the filaments into a bundle of contiguous filaments while they still contain a portion of the solvent of said solution, drawing said bundle of contiguous filaments through a zone in which they are heated at elevated temperatures at which solvent contained in the bundle of filaments is evaporated into a gaseous atmosphere in said zone and the filaments bond together into a unitary monofil without application to said bundle of external pressure forcing the filaments together, said filaments being gathered at a point at which they contain sufiicient solvent to cause the individual filaments to bond together by said evaporation of solvent during said heating into a unitary monofil which retains the aforesaid corrugated surface configuration of a bundle of contiguous filaments, and cutting the monofil into short lengths,

10. Bristles of claim 9 in which the polymer is a copolymer of methacrylonitrile and acrylonitrile copolymerized in the ratio of 10/90 to 30/70 by weight of methacrylonitrile/acrylonitrile.

11. Bristles of claim 9 in which the polymer is polyacrylonitrile.

12. Tapered bristles of a polymer of acrylonitrile containing at least 70% acrylonitrile and the remainder substantially consisting of an arcylic compound polymerizable therewith, said bristles having a diameter of 0.5 to 50 mils, with the body of the individual bristles having a homogeneous structure of said polymer and the corrugated surface configuration of a bundle of numerous contiguous filaments extending lengthwise from end to end of the bristle, and the bristle in cross-section having a scalloped outline, said homogeneous structure within the body of said bristles having been formed by spinning numerous separated filaments from a solution of said polymer in a volatile solvent therefor, partially removing solvent from the separated filaments, gathering the filaments into a bundle of contiguous filaments while they still contain a portion of the solvent of said solution, heating said bundle of contiguous filaments in a gaseous atmosphere at elevated temperatures and thereby evaporating solvent from the bundle of filaments, said filaments being gathered at a point at which they contain sufiicient solvent to cause the individual filaments to bond together by said evaporation of solvent during said heating into a unitary monofil which retains the aforesaid corrugated surface configuration of a bundle of contiguous filament without external pressure forcing the filaments together being applied to the bundle of filaments, continuously passing said monofil through a heating zone in which short portions of the monofil successively passed therethrough are heated, stretching the thus heated monofil, periodically changing the amount successive portions of the monofil are stretched, thereby stretching the monofil to molecularly orient it and forming along its length alternating sections of large and small thickness with the monofil tapering from one to the other of these sections, and cutting the monofil at its points of smallest diameters to form tapered bristles.

13 Bristles of claim 12 in which the polymer is a copolymer of methacrylonitrile and acrylonitrile copolymerized in the ratio of 10/90 to 30/70 by weight of methacrylonitrile/acrylonitrile.

14. Bristles of claim 12 in which the polymer is polyacrylonitrile.

FRANCOIS J. G. OLMER. GLENN A. NESTY.

References Cited in the file of this patent UNITED STATES PATENTS OTHER, REFERENCES The Journal of the Society of Dyers and Colourists, vol. 65, No. 10, October 1949, pages 472- 73. 

9. BRISTLES OF A POLYMER OF ACRYLONITRILE CONTAINING AT LEAST 70% ACRYLINITRILE AND THE REMAINDER SUBSTANTIALLY CONSISTING OF AN ACRYLIC COMPOUND POLYMERIZABLE THEREWITH, SAID BRISTLES HAV- 